In a controller with many ports, how the controller behaves under high load conditions is a consideration during design. Even when the average load is light, randomness in the arrival of requests can cause transient high load conditions to occur. Occasionally many, and perhaps all, of the requests can be simultaneously active.
A problem with servicing a large number of simultaneous requests is that each request is delayed by the requests serviced before it. All requests need to be serviced before any buffers overflow and before any real time deadlines are reached. In a complex system, designing a fixed set of priorities that ensures that all requests will be serviced in time can be difficult or impossible.